Packing



March 5, 1935. R. J. s. PIGOTT 1,993,721

PACKING Filed Jan. 11, 1934 2 Sheets-Sheet 1 March 5, 1935. J, 5,Plea-r1" PACKING 2' Sheets-Sheet 2 Filed ,Jan. 11, 1934 Patented 'ar.i935 PATENT OFFICE 'racxme Reginald J. s. Pigott, Pittsburgh, Pa.-,assignor to Gulf Research & Development Co p ation, Wilmington, Del., acorporation of Delaware Application January 11, 1934, Serial No. 706,265

Claims. (Cl. 1ll3-126) This invention relates to packing; and itcomprises in a rotary pump or motor having a rotor rotatably mounted ina stationary casing and adapted to cooperate with a portion of thecasing 5 to form a pressure holding chamber, improved packing means formaintaining a pressure .tight seal between the rotor and the casingwithout excessive binding on the rotor, said means comprising a floatingmetal packing member engaging the rotor and adapted to be forced thereagainst by pump pressure and a flexible backing member'between thecasing and the packing member and adapted to reduce, in regulableamount, the force exerted on the packing member by pump pressure in thepressure chamber, so as to provide a tight packing seal for the pressurechamber without excessive frictional binding; all as more fullyhereinafter set forth and as claimed.

In recent years there has been developed a new type of rotary pumpcomprising a ring gear, with internal teeth, and a cooperating pinion,with external teeth, the combination being mounted in a suitable portedcasing and the gears being adapted to be revolved either by the ringgear or by the pinion. The teeth are so designed that the teeth andtooth spaces of the meshing gears form a series of gradually expandingclosed chambers during part of a revolution and a series of graduallycontracting closed chambers during another part of the'revolution; andthe ports are so arranged that .the expanding chambers serve to suckfluid from an inlet and the contracting chambers serve to expel fluidthrough an outlet.

This type of pump presents many advantages over reciprocating pumps,vane pumps, double pinion pumps and other common designs. Thering-gear-pinion type has high volumetric and mechanical emciency, issimple in design, and can readily be modified for use either as a pumpor a gas compressor. It may be used as a motor without change.

In my copending application Serial No. 626,420,

- filed July 30, 1932, I have disclosed particularly advantageous formsof ring-gear-pinion pumps and compressors, in which the expandingchambers draw in fluid for almost a full half revolution, and expel itfor almost a half revolution. In

I these pumps the ring gear has one more tooth than the pinion, and theteeth are in continuous sliding contact.

In those pumps the ring gear and the outlet side of the casing cooperateto form a pressure holding chamber, the ring gear and the pressurechamber being sealed off from the rest of the casing and the bearings..Capillary seals or halffling'devlceswh'ereinthe liquid forming the sealmust pursue a meandering course in order to escape, aresatisfactory,in=pumping liquids not 5 excessively thin and at moderate speeds andpressures. These pumps are adapted to develop high pressures (up toseveral hundred'pounds per square inch in a single pump) and work athigh peripheral speeds of the ring gear.

f According to the'present' invention packing means are provided whichare adapted to form a tight seal between ring gear and easing under the.conditions of pumping most apt to cause leakage, as when thin (that is,low viscosity) liquids are pumped at high pressures and speeds. Myinvention comprises a packing member actually making pressure contactwith the rotor. In using simple spring rings or floating bands aspackers between ring gear and casing it is practically inevitable thatthepacker is under full pump discharge pressure, causing it to pressheavily on the ring gear when the pump pressures are high. Accordingly,in the use of such packing members, diillculties are met with because of(1) the high peripheral speed, that is, rubbing speed, of the rotor,which tends to produce excessive wear and friction with the packing, and(2) the high pressure in' the pressure chamber in the outlet side of thepump, which tends to force the packing member against the rotor with apressure which may be as great as 700 or 800 pounds per square inch inhigh pressure pumping. This pressure is in excess of that required foreffecting a tight seal and is too great for as satisfactory bearingconditions. I flnd that in using ordinary cast iron or babbit faced snaprings and sealing strips in sealing the ring gear from the casing,excessive wear and frictional resistance are aptto occur under theextreme pumping conditions described. Soft packings, while satisfactoryat moderate pump speeds and pressures, generally fail at high speeds.

I have found that an excellent seal between rotor and casing in highspeed, high pressure pumps may be obtained, without substantialfrictional resistance and wear, by using a metal packing member mountedin arecess in the casing and in contact with the rotor, forced againstthe rotor with a moderate, regulable pressure, the pressure useddepending upon the discharge pressure of the pump, and being less thanthe discharge pressure. I utilize the discharge pressure of the pump toforce the packing member against the rotor, and I reduce the netpressure of the 65 packing member on the rotor by reducing the fluidpressure on the back of the packing member (against which the pumpoutlet pressure is exerted). I do this by partially filling up thepressure cavity in the recess between the packing member and the casing,with a flexible partition or dia-- phragm; or by means of a backingfilling of soft, readily deformable material of the nature of softrubber or Thiokol (a synthetic rubber imper-- vious to oils). I canregulate the pressure of the packing member froma small fraction of theoutlet pressure, to as near the outlet pressure as desired, by varyingthe area of the edge 01 the rubber exposed to the fluid pressure; or inthe case of the partition, by arranging the partition to cut ofi agreater or less proportion of the packing member from access to pumppressure.

In the accompanying drawings I have shown,

my packing means using a metal packing strip and a rubber filler;

Fig. 2 is a perspective view of the packing means oi. Fig. 1;

Fig. 3 is a view in section along the line A-A 01. Fig. 1; 1

Fig. 4 is a view in section of the pump of Fig. 1 along the line A--A,showing a modified form of the packing means of Fig. 1;

Fig. 5 is a view similar to Fig. 3 showing a modifled form of packingmeans using a metal diaphragm or partition;

Fig. 6 is a view similar to Fig. 3 of a modified form of packing meansusing a metal partition unattached to the packing strip; and

Fig. 7 is a sectional view taken along line 3-43 of Fig. 1, the rotorbeing shown in elevation.

In these showings, in which like reference numerals indicate like partsthroughout, Figs. 1 and '7 show in section a gear pump comprising acasing 1 having an inlet 2 and outlet 3. In the casing are mounted ringgear 4 and pinion 5, the gears being parallel and eccentric as shown.Pinion 5 is mounted on a driving shaft 5A. The ring gear has one moretooth than the pinion, and the tooth shapes on the gears are such thatthe teeth are in continuous sliding contact, forming a series ofchambers 6 which expand for half a revolution and contract for te restof the revolution. The ring gear is provided with ports 6A incommunication with the chambers 6. The expanding chambers are incommunication with the in-- let through the annular chamber '7, and thecontracting chambers are in communication with the outlet through thepressure holding chamber 8. As-the gears turn in the direction indicatedby arrows, liquid is taken from the inlet and forced a through theoutlet under pressure.

such as crude oil; but such packing means tend to. allow leakage whenthin liquids are pumped at high speeds and pressures. Sort packing andplain snap rings or the like are not satisfactory for the reasons givenante.

According to the present invention 1 provide packing means for the ringgear comprising a curved metallic strip 9 fitting the periphery of thering gear and mounted in a recess 10 in ends of the casing as shown, thethickness of the strip being less than that of the recess. The strip hasa slot-like opening 11 as shown equal in size and shape to the openingof pressure holding chamher 8. This strip is made of metal selected. forlow frictional resistance and good Wearing qualities, whichmetal mayadvantageously be nitrided steel, babbitt-faced steel, or Graphalloy(graphite and brass). As shown, this strip engages the outlet side ofthe ring gear and also extends into the abutments of the casing.

If the strip were used alone, the back of the strip and the recess wouldbe in direct communication with the pressure holding chamber 8, and thefull discharge pressure or the pump would be exerted on the strip toforce it against the rotor. At high pressures, the strip might be forcedagainst the ring gear with sufiicient iorce to cause seizure; in anycase, with excess force over that needed for effecting a seal.

To moderate the pressure of the strip on ends of the rotor, in theembodiment shown in Fig. 1, 1 provide a soft rubber filling 12 in therecess between the strip and the casing. The dimensions of the strip andcavity are such that the area of the edge 13 of the filler is less thanthe area of the strip. Pressure in the chamber 8 acts only on the edge14 01 the metal strip and the edge 13 of the filler. The pressure forcesthe soft rubber to fit the cavity tightly and with a perfect seal allaround the edges. The pressure on the back of the sealing strip isreduced in a ratio equal to that of the area 01' the filler to the areaor the back of the strip. By changing the ratio or the area of the stripto the edge area or the filler, as by using a thicker strip and athinner filler, for instance, the pressure exerted by the arcuatesealing strip on the ring gear may be varied as desired. 2

As best shown in Fig. 7 the metal strip 9 completely surroundsthedischarge passage 3 at its boundary adjacent the ring gear 4, the portor opening 11 coinciding with the opening in the discharge passage toafford communication between the chamber 6 and the outlet of the pump.

The filler may be made of other materials than soft rubber, such asThiokol for instance. The requirement is that the material should beplastic, resilient and impervious and resistant to attack by the fluidbeing pumped.

In Fig. 4, I have shown a modified form of filler 12' having a cut outslot or groove 15 as shown. This allows access of fluid under pressureto a portion of the filler and hence a greater pressure will be exertedon the sealing strip. This modiflcation is useful when the dischargepressure oi the pump is relatively low. By slotting or grooving thefiller the pressure on the sealing strip may be increased without havingto increase the thickness of the flller.

In the modification of Fig. 5 a partition or diaphragm i6,advantageously or thin, springy metal, is substituted for the rubberfilling. This partition may be likened to a single convolution of astraight edged bellows. It is attached to the strip and to the casing bysoldering or brazing as at 17. The partition serves to shut off aportion 0! the area of the back of the sealing strip, thus reducing thenet pressure exerted by Pill] hill weaver the strip on the ring gear toa value below the discharge pressure the pump.

In Fig. 6 is shown a modified partition which comprises a thin flexiblemetallic partition 18 slightly dished as shown, and fastened by rivetingor soldering as at 19 to the casing. One edge of the strip simply restson the sealing strip as shown, and is held tightly thereto by fluidpressure during operation of the pump.

It will be seen that I have provided simple packing means formaintaining a seal between a rotor and stator in a rotary pump. Thepressure or the packing means is readily adjustable. My invention isillustrated in its application to a gear pump, but it is useful foreffecting seals in similar relations in other devices such as multistagecentrifugal pumps, turbines and hydraulic motors, and in rotary pressuredevices generally.

What I claim is:

1. In a rotary pressure device having a rotor rotatable in a casing andadapted to cooperate with one portion of the casing to form apressureholding chamber in communication with an arcuate portion of theperiphery of the rotor and with another portion oi the casing to form aseparate chamber in communication with another arcuate portion of theperiphery of the rotor, improved packing means between the rotor and thefirst-named portion of the casing com, prising a floating arcuatemetallic sealing member engaging the portion of the periphery of therotor in communication with the pressure holding chamber, the casingbeing provided with a recess in which the member is positioned, thesealing member being forced against the rotor under fluid pressure fromthe pressure holding chamber, and means for limiting the area of thesealing member exposed to said pressure, so that the net pressureexerted by the sealing member on the rotor is less than the pressureexisting in the pressure holding chamber.

2. In a rotary pressure device having a rotor rotatable in a casing andadapted to cooperate with one portion of the casing to form a pressureholding chamber in communication with an arcuate portion of theperiphery of the rotor and with another portion or the casing to form aseparate chamber in communication with another arcuate portion of theperiphery of the rotor, improved packing means between the rotor and thefirst-named portion of the casing comprising a floating arcuate metallicsealing strip in contact with the portion of the periphery of the rotorin communication with the pressure holding chamber, the casing beingprovided with an arcuate recess in which the strip is positioned, thestrip being forced against the rotor under fluid pressure from thepressure holding chamber, and means ror limiting the pressure on theback of the strip to reduce the pressure of the strip against the rotor,said means comprising flexible means in the recess in contact with thestrip and the casing and adapted to close off a portion of the area ofthe back of the strip from the direct pressure of the pressure chamber.

3. The packing means of claim 2 wherein the means for reducing thesealing strip pressure comprises an arcuate rubber filling in the recessbetween the strip and the casing, the area of the edge of the fillingbeing presented to the pressure in the pressure holding chamber and thisarea being less than the area of the back of the sealing strip wherebythe pressure on the sealing strip is reduced in inverse ratio to saidareas.

4. The packing'means of claim 2 wherein the means for reducing thesealing strip pressure comprises a rubber filling in the recess betweenthe strip and the casing, the filling having a slot in its edge open tofluid pressure in the chamber, the slot extending only part way throughthe filling, so that the pressure on the sealing strip is less than thefluid pressure. I

5. The packing means of claim 2 wherein the means for reducing thesealing strip pressure comprises an arcuate, flemble, thin metallicdiaphragm in the recess between the strip and the casing, the diaphragmbeing in contact with the casing and the strip and being adapted to shutoff a portion of the area of the strip from access to the pressure inthe pressure holding chamber. 6. The packing means of claim 2 whereinthe means for reducing the sealing strip pressure comprises an arcuate,flexible, thin, folded metallic diaphragm in the recess between thestrip and the casing and attached to the strip and to the casing, andbeing adapted to shut 0d a portion of the area of the strip from accessto the pressure in the pressure holding chamber.

'1. The packing means of claim 2 wherein the means for reducing thesealing strip pressure comprises an arcuate, thin, flexible metallicdiaphragm in the recess between the strip and the casing, attached tothe casing and resting on the strip, and being adapted to shut off aportion of the area of the strip from access to the pressure in thepressure holding chamber.

8. An improved rotary pressure device comprising a pumping rotor, astator provided with a chamber extending arcuately over a portion of theperiphery of the rotor, a pressure holding chamber extending arcuatelyover another portion of the periphery of the rotor and provided with anarcuate recess in the pressure holding chamber adjacent the periphery ofthe rotor, said recess terminating in an abutment at each end,

the abutments separating and defining the said enclosing the pumpingrotor and provided with.

a chamber extending arcuately over a portion of the periphery of therotor, a pressure holding chamber extending arcuately over anotherportion or the periphery of the rotor and provided with and having anarcuate recess adjacent the periphery of the rotor at each end thereof,an arcuate packing member in the recess and engaging the peripheral endportions of the rotor and provided with a slot-like opening registeringwith the middle portion of the rotor, and a similarly shaped yieldablebacking member having a slotlike opening registering with the opening insaid packing member, the backing member being positioned in the recessbetween the packing memher and the stator and forming a seal betweenbetween the rotor and the casing comprising a ported metallic sealingmember surrounding said fluid passage at the'boundary adjacent therotor, the casing being provided with a recess in which the member ispositioned, the back of the sealing member being in communication withfluid pressure from the passage so that said pressure acts to hold thesealing member against the rotor and a member for variably limiting thearea of the back of the sealing member exposed to said pressure so thatthe net pressure exerted by the sealing member on the rotor may bereduced in controlled amounts under:the pressure existing in 5 saidfluid passage.

REGINALD J. S. PIGO'I'I.

